A high voltage battery for power driving, an inverter device for driving a motor by converting the DC high voltage output of the high voltage battery into an AC high voltage output, and a DC-DC converter device for supplying electric power to low voltage loads such as lamps and a radio of a vehicle by converting the DC high voltage output of the high voltage battery into a DC low voltage output, and the like are mounted on the vehicle such as a hybrid vehicle, a plug-in hybrid vehicle, or an electric vehicle.
A DC-DC converter device includes: a high voltage switching circuit for converting a DC high voltage into an AC high voltage; a transformer for converting the AC high voltage into an AC low voltage; a low voltage switching circuit for converting the AC low voltage into a DC low voltage; a filter circuit for reducing the propagation of noises generated from the DC-DC converter device to the outside; and a control circuit for generating control signals for controlling the switching circuits. A DC-DC converter device has a problem in that there is a possibility that electromagnetic noises leaking from switching circuits and a transformer propagate to a filter circuit and a control circuit with the result that electromagnetic couplings are induced.
The following structure is known as a structure capable of suppressing the propagations of electromagnetic noises.
The structure is described as configured in such a way that a shield wall is installed on a metal chassis for shielding an output filter from a voltage-boost/high-voltage circuit section including switching elements, and a metal base plate is fastened to the upper surface of the shield wall, and owing to this structure, radiation noises emitted from the switching elements are absorbed by the shield wall, so that electromagnetic noises that are superimposed on the output filter can be reduced. In addition, in this structure, a first shield wall that shields an output filter from switching elements is installed, and a second shield wall that separates the output filter from an output terminal and a bus bar is installed on the base plate as well. The second shield wall is disposed between the output filter and the output terminal, and the output filter is disposed between the first shield wall and the second shield wall (for example, refer to FIG. 9 in Patent Literature 1).